Background

Temporal variation of temperature-health associations depends on the combination of two pathways: pure adaptation to increasingly warmer temperatures due to climate change, and other attenuation mechanisms due to non-climate factors such as infrastructural changes and improved health care. Disentangling these pathways is critical for assessing climate change impacts and for planning public health and climate policies. We present evidence on this topic by assessing temporal trends in cold- and heat-attributable mortality risks in a multi-country investigation.

Methods

Trends in country-specific attributable mortality fractions (AFs) for cold and heat (defined as below/above minimum mortality temperature, respectively) in 305 locations within 10 countries (1985–2012) were estimated using a two-stage time-series design with time-varying distributed lag non-linear models. To separate the contribution of pure adaptation to increasing temperatures and active changes in susceptibility (non-climate driven mechanisms) to heat and cold, we compared observed yearly-AFs with those predicted in two counterfactual scenarios: trends driven by either (1) changes in exposure-response function (assuming a constant temperature distribution), (2) or changes in temperature distribution (assuming constant exposure-response relationships). This comparison provides insights about the potential mechanisms and pace of adaptation in each population.

Results

Heat-related AFs decreased in all countries (ranging from 0.45–1.66% to 0.15–0.93%, in the first and last 5-year periods, respectively) except in Australia, Ireland and UK. Different patterns were found for cold (where AFs ranged from 5.57–15.43% to 2.16–8.91%), showing either decreasing (Brazil, Japan, Spain, Australia and Ireland), increasing (USA), or stable trends (Canada, South Korea and UK). Heat-AF trends were mostly driven by changes in exposure-response associations due to modified susceptibility to temperature, whereas no clear patterns were observed for cold.

Conclusions

Our findings suggest a decrease in heat-mortality impacts over the past decades, well beyond those expected from a pure adaptation to changes in temperature due to the observed warming. This indicates that there is scope for the development of public health strategies to mitigate heat-related climate change impacts. In contrast, no clear conclusions were found for cold. Further investigations should focus on identification of factors defining these changes in susceptibility.

中文翻译：

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气候变化下冷热潜在适应机制的多国分析

背景

温度-健康关联的时间变化取决于两种途径的组合：纯粹适应由于气候变化导致的日益变暖的温度，以及由于基础设施变化和改善医疗保健等非气候因素导致的其他衰减机制。解开这些路径对于评估气候变化影响以及规划公共卫生和气候政策至关重要。我们通过评估多国调查中由冷和热引起的死亡风险的时间趋势来提供有关该主题的证据。

方法

使用两阶段时间序列设计估计了 10 个国家（1985 年至 2012 年）内 305 个地点的冷和热（分别定义为低于/高于最低死亡率温度）的国家特定归因死亡率分数 (AFs) 趋势时变分布式滞后非线性模型。为了区分纯适应对温度升高和对热和冷的敏感性（非气候驱动机制）的主动变化的贡献，我们将观察到的年度 AF 与在两种反事实情景中预测的结果进行了比较：由任一 (1) 变化驱动的趋势暴露-响应函数（假设恒定的温度分布），（2）或温度分布的变化（假设恒定的暴露-响应关系）。

结果

除澳大利亚、爱尔兰和英国外，所有国家与热相关的 AF 均有所下降（在第一年和最后 5 年期间分别从 0.45-1.66% 降至 0.15-0.93%）。发现了不同的感冒模式（其中 AFs 的范围从 5.57-15.43% 到 2.16-8.91%），呈现下降（巴西、日本、西班牙、澳大利亚和爱尔兰）、上升（美国）或稳定趋势（加拿大、韩国）和英国）。热-AF 趋势主要是由于对温度的敏感性改变而导致的暴露-反应关联的变化，而没有观察到冷的明显模式。

结论

我们的研究结果表明，在过去的几十年中，热死亡率的影响有所下降，远远超出了纯粹适应由于观察到的变暖导致的温度变化所预期的影响。这表明存在制定公共卫生战略以减轻与热相关的气候变化影响的空间。相比之下，对于感冒没有明确的结论。进一步的调查应侧重于确定定义这些易感性变化的因素。